Abstract
The tri-spine horseshoe crab, Tachypleus tridentatus, is a threatened species that inhabits coastal areas from South to East Asia. A Conservation management system is urgently required for managing its nursery habitats, i.e., intertidal flats, especially in Japan. Habitat suitability maps are useful in drafting conservation plans; however, they have rarely been prepared for juvenile T. tridentatus. In this study, we examined the possibility of constructing robust habitat suitability models (HSMs) for juveniles based on topographical data acquired using unmanned aerial vehicles and the Structure from Motion (UAV-SfM) technique. The distribution data of the juveniles in the Tsuyazaki and Imazu intertidal flats from 2017 to 2019 were determined. The data were divided into a training dataset for HSM construction and three test datasets for model evaluation. High accuracy digital surface models were built for each region using the UAV-SfM technique. Normalized elevation was assessed by converting the topographical models that consider the tidal range in each region, and the slope was calculated based on these models. Using the training data, HSMs of the juveniles were constructed with normalized elevation and slope as the predictor variables. The HSMs were evaluated using the test data. The results showed that HSMs exhibited acceptable discrimination performance for each region. Habitat suitability maps were built for the juveniles in each region, and the suitable areas were estimated to be approximately 6.1 ha of the total 19.5 ha in Tuyazaki, and 3.7 ha of the total 7.9 ha area in Imazu. In conclusion, our findings support the usefulness of the UAV-SfM technique in constructing HSMs for juvenile T. tridentatus. The monitoring of suitable habitat areas for the juveniles using the UAV-SfM technique is expected to reduce survey costs, as it can be conducted with fewer investigators over vast intertidal zones within a short period of time.
Highlights
Horseshoe crabs are a type of estuarine chelicerate arthropods (Chelicerata) that are known as “living fossils” because they have existed for over 200 million years [1]
Our study aimed to examine the possibility of constructing a robust habitat suitability models (HSMs) for juvenile T. tridentatus with topographical data acquired using the UAV-SfM technique, and to create habitat suitability maps of the Tsuyazaki and Imazu intertidal flats
Test data 1, Test data 2, and Test data 3 were used to evaluate the robustness of the models with the highest sensitivity (GLM00 and Maxent20) and the models with the highest area under the receiver-operating characteristics curve (AUC)
Summary
Horseshoe crabs are a type of estuarine chelicerate arthropods (Chelicerata) that are known as “living fossils” because they have existed for over 200 million years [1]. The blood of horseshoe crabs is commercially used in medicine, and their eggs are an important food source for migratory shore birds and eels [4,5]. They are useful as a flagship species to spread public awareness regarding biodiversity conservation [6]. The conservation of horseshoe crabs is ecologically and commercially important, and it is receiving increased global attention [6,8,9,10] Progress in this field of study may contribute to the sustainable management of estuarine ecosystems
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